Among cardiovascular diseases (CVD), coronary artery disease (CAD) is regarded as the main cause of a sudden death. The pathological changes caused by coronary artery disease (CAD) include stenosis and even occlusion of coronary arteries for supplying oxygen and nutrients to the heart, thereby damaging cardiac tissues. Depending on the degree of severity, coronary artery disease (CAD) has different manifestations, namely angina, myocardial infarction, and sudden cardiac death. Angina is chest pain due to ischemia (a lack of blood, thus a lack of oxygen supply) of the heart muscle and typically occurs when the weather is cold or when the patient is mentally or physically overburdened or has an overstretched stomach. Myocardial infarction is worse than angina, because the underlying pathological change typical of myocardial infarction is irreversible damage of the heart muscle. Myocardial infarction ends up in a heart failure, when it is severe. In a worst-case scenario, the consequence of myocardial infarction is a sudden cardiac death, wherein the victim goes into shock and dies as soon as arrhythmia halts the heart and decreases the cardiac output greatly. Hence, coronary artery disease (CAD) is dubbed an invisible killer because of its symptomless insidious course. Coronary artery disease (CAD) is seldom diagnosed with a static electrocardiogram (static ECG), as it starts to alert a patient only when cardiac hypoxia happens to the patient.
At present, diagnosis tools in wide use for diagnosing coronary artery disease (CAD) include treadmill ECG, Thallium scan, and CT-angio. However, the application of the aforesaid diagnosis tools is limited by size, costs, and methodology of measurement, regardless of whether the diagnosis tools are used at hospital or at home. In this regard, the prognosis of coronary artery disease (CAD) is often evaluated by means of conventional ECG signals, albeit with a drawback—providing just 12 channels which are restricted to longitudinal cross-sections and transverse cross-sections of the heart. Although the equipment required for providing the 12-channel ECG signals is simple and easy to operate, its spatial resolution is inadequate, not to mention that it provides a limited amount of information pertaining to the analysis and identification of related symptoms, thereby restricting its application and analysis. Furthermore, although high-resolution magnetocardiography (MCG) provides sufficient spatial information, it is not in wide use because of its high prices and large size.